udevadm

You can use udevadm to see the variables set by udev for a device. This is helpful if you want to get information about the device, based on whether it has a DVD or a CD in there, for example.

udevadm info /dev/sr0

If you want to change any rules, such as in /lib/udev/rules.d or /etc/udev/rules.d, you can reload them with udevadm as well:

udevadm trigger

That's what I use when doing my onevent trayclose calls.

In /etc/udev/rules.d/70-persistent-cd.rules I generate a symlink to /dev/dvd and /dev/bluray, as well as call onevent.trayclose when there is a DVD detected in the drive on an event change (tray closed from being open).

# Sony Blu-ray
SUBSYSTEM=="block", ENV{ID_MODEL}=="ATAPI_iHOS104", ENV{ID_REVISION}=="WL0D", SYMLINK+="bluray", ENV{GENERATED}="1"
SUBSYSTEM=="block", ENV{ID_MODEL}=="ATAPI_iHOS104", ENV{ID_REVISION}=="WL0D", SYMLINK+="dvd", ENV{GENERATED}="1"
SUBSYSTEM=="block", ENV{ID_MODEL}=="ATAPI_iHOS104", ENV{ID_CDROM_MEDIA_DVD}=="1", ENV{ID_CDROM_MEDIA_STATE}=="complete", RUN+="/usr/local/bin/onevent.trayclose"